Rotary bore hole air hammer drive mechanism

ABSTRACT

A hammer piston reciprocates in a housing and impacts against an anvil in the housing which is integral with a drill bit, a drilling string rotating the housing during the repeated impacting of the piston against the anvil. Torque is transmitted from the housing through a plurality of segments and a drive member to the anvil during the impacting action, transmission of the torque by the segments being effected through generally radial or off radial surfaces formed on the anvil and the segments which are perpendicular to the tangent of the drive so that the surfaces do not cam the segments outwardly against the housing.

United States Patent Curington Feb. 18, 1975 ROTARY BORE HOLE AIR HAMMERDRIVE MECHANISM Inventor:

US. Cl 173/73, 64/23, 173/78, 173/80, 173/131 Int. Cl. E210 1/12 Fieldof Search 173/17, 73, 78, 80, 64, 173/131, 132, 133; 403/356, 358; 64/23References Cited UNITED STATES PATENTS 9/1971 Curington 173/17 X..173/73 10/1971 Martini 12/1971 Vincent Primary ExaminerErnest R,Purser Assistant ExaminerWilliam F. Pate, lll Attorney, Agent, orFirmBernard Kriegel [57] ABSTRACT A hammer piston reciprocates in ahousing and impacts against an anvil in the housing which is integralwith a drill bit, a drilling string rotating the housing during therepeated impacting of the piston against the anvil. Torque istransmitted from the housing through a plurality of segments and a drivemember to the anvil during the impacting action, transmission of thetorque by the segments being effected through generally radial or offradial surfaces formed on the anvil and the segments which areperpendicular to the tangent of the drive so that the surfaces do notcam the segments outwardly against the housing.

19 Claims, 5 Drawing Figures ROTARY BORE HOLE AIR HAMMER DRIVE MECHANISMBACKGROUND OF THE INVENTION The present invention relates to drill bitapparatus for drilling a bore hole in a formation, and more particularlyto pneumatically operated apparatus that imparts a percussive action toan anvil and drill bit integral therewith while the latter arepreferably rotated.

During the impacting action of an air hammer piston against the anvilportion of a drill bit, the anvil and drill bit are rotated by rotatingthe housing of the apparatus, so that the face of the drill bit coverssubstantially the full area of the bottom of the bore hole being drilledin a formation, torque being transmitted from the housing to the anvilin certain well known apparatus through a key and keyway type of splineconnection, in which a multiplicity of elongate keys and keyways aredisposed circumferentially around the anvil and housing memberassociated therewith. Such key and keyway spline interconnections fortransmitting torque between the housing and the anvil effect asubstantial reduction in the cross-sectional area of the anvilthroughout the length of the key and keyway portion, which results inloss of the air hammer energy transmitted throughout the length of theanvil and bit. This is believed to be due to the fact that the impactingof the hammer piston against the anvil creates longitudinal stresspulses which travel through the bit from the anvil end to the face endof the bit, which stress pulses or stress waves remain constant inmagnitude until such time as they encounter a change in cross-sectionalarea of the bit, and at these changes in cross-sectional area, part ofthe pulse is reflected back and a smaller magnitude pulse continues inthe original direction.

The pending application for U.S. Pat. Ser. No. 239,047, now U.S. Pat.No. 3,804,181 filed Mar. 29, 1972, discloses a torque transmittingspline type of drive between the housing and the anvil and bit, whichhas a laser decrease in cross-sectional area throughout its length thanin the prior bits, resulting in a substantial decrease in the amount ofenergy lost through the bit as a result of reflections created by thetransmitting of the longitudinal stress pulses from the upper end of theanvil to the lower drilling face of the bit. In addition,

the torque transmitting drive connection provided between the housing,usually a housing sub or member forming the lower end of the housing,and the anvil can be manufactured at a substantially reduced cost. Wearbetween the anvil and the torque transmitting parts engaging it is moreuniform, such that the drive connection between the housing and anvilhas a much longer life than prior types of drives, such as the key andkeyway types heretofore used. Moreover, when wear does occur, the partsare readily replaceable, such parts requiring replacement beingcomparatively few in number and relatively inexpensive.

Nothwithstanding the foregoing advantages in this prior bore hole airhammer, wearing in, fit, and service problems can be encountered underthe conditions of use of such apparatus, if the field operator iscareless. In addition, the self-energizing clutch-like characteristic ofthe drive mechanism makes it difficult, requiring very high torque tobreak out the threaded connection between the drive sub and the housing.

SUMMARY OF THE INVENTION The present invention provides a rotary borehole air hammer with a drive mechanism which has the advan-' tages ofthe air hammer of the aforesaid pending application, but which hasfurther advantages in terms of manufacturing tolerances,simplicity ofservice and repair, as well as operation.

More particularly, the present invention provides a rotary bore hole airhammer having a drive mechanism which retains the torque transmittingcharacteristics of a splined connection while utilizing loose drivesegments, but wherein the housing is not subjected to internal damage,such as gelling, and the drive sub is eas ily removed from the housing,since the drive segments and the companion recesses are soconstructedthat high radial reaction forces are not generated during use ordisassembly of the apparatus.

In accomplishing the foregoing, a driver and key structure is utilizedwherein torque is transmitted through the keys, to the anvil, from thehousing through near radial or slightly off radial, i.e., substantiallyradially extended surfaces, such that the forces transmitted do not tendto cam the segments outwardly.

In a specific form the segment and anvil surfaces are arranged so as tonot apply a cam action to the segments in either direction, the surfacesbeing perpendicuular to the tangent of the anvil and housing. In thisform the substantially radial surfaces are, thus, not truly radial butare parallel to one another and to a radial plane which is slightlyoff-set, to one side of the median plane of the segment to provide alarger contact area in the direction of drive when drilling than whenthe apparatus is being disassembled.

This invention possesses many other advantages and has other objectswhich may be made more clearly apparent from a consideration of a formin which it may be embodied. Such a form is shown in the drawingsaccompanying and forming part of the present specification. It will nowbe described in detail for the purpose of illustrating the generalprinciples of the invention; but it is to be understood that suchdetailed description is not to be taken in a limiting sense.

Referring to the. drawings:

FIGS. 1a and lb together constitute a longitudinal section through anapparatus embodying the invention, with parts in their relativepositions in which the hammer piston has completed delivering an impactblow against its companion anvil and the drill bit secured thereto, FIG.lb being a lower continuation of FIG. 1a;

FIG. 2 is a cross-section taken along the line 22 on FIG. lb;

FIG. 3 is a longitudinal, fragmentary section taken along the line 3-3on FIG. 2; and

FIG. 4 is an isometric view of one of the drive segments.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings an airhammer apparatus A is provided that is secured to the lower end of astring of drill pipe B, by means of which the apparatus is rotated tocorrespondingly rotate an impact anvil bit C used for drilling a borehole D, the apparatus delivering repeated impact blows upon the anvilbit when compressed air is forced down the drill pipe for actuating theapparatus and for cleaning the cuttings from the bottom E of the hole.The apparatus is relatively simple, consisting of an elongate housingstructure that includes an upper sub 11 having an upper threaded box 12(or threaded pin, not shown) for threaded attachment to the lower end 13of the string of drill pipe, that extends to the drilling rig (notshown) at the top of the bore hole D. This sub is threadedly secured tothe upper portion of an elongate housing section 14, which can be of onepiece, the lower end of which is threadedly secured to a lower housinghead or drive member 15, the lower end 16 of the housing section bearingagainst an upwardly shoulder 17 formed on the head.

An elongate anvil portion 18 of the anvil bit C is piloted upwardlywithin the drive member and lower portion 19 of the housing section 14,a hammer piston 20 being reciprocable in the housing section above theanvil 18 to deliver repeated impact blows thereagainst. The anvil ispreferably formed integrally with the drill bit portion 21 of the anvilbit, and which has suitable cutting elements 22 (such as sinteredcarbide buttons, not shown) mounted in its drilling face 23 forimpacting against the bottom E ofthe bore hole, to produce cuttingstherein, the cutting elements 22 also acting against the side of thebore hole adjacent to its bottom to insure the production of a bore holeD of the desired diameter.

During the reciprocation of the hammer piston 20 in the housing todeliver impact blows upon the anvil bit, the drill pipe string B andhousing structure 10 are rotated at a desired speed, such as 20 r.p.m.,to correspondingly rotate the anvil bit C and insure an impacting actionof the cutting members 22 over substantially the entire cross-sectionalarea of the bottom E of the hole. During the impacting action, suitabledrilling weight is imposed on the anvil bit through the drill pipestring B and the housing structure 10, such drilling weight beingtransferred from the lower end 24 of the housing head or drive member 15to an upwardly facing shoulder 25 of the bit 21. The rotary drive itselfis transferred from the housing structure 10 to the anvil 18 through aslidable spline type of connection 26, which is made in accordance withthe invention and will be later described.

In general, the upper portion of the anvil has circumferentially spacedelongate recesses, in which drive segments 28 are disposed, thesesegments being carried in circumferentially spaced windows 29 in thedrive member 15. The recesses 27 are substantially longer than thelength of the segments 28, permitting relative longitudinal movement ofthe anvil bit C with respect to the housing structure 10. The rotaryeffort is transferred from the housing section 14 to the drive member 15by virtue of the threaded connection 30d, and from the sides 29a of theopenings or windows 29 to the segments 28, from where the turning effortis transmitted through the abutting segment surfaces 27a on the segments28 and anvil surfaces 27 to the anvil 18 of the bit C.

The housing section 14 includes an elongate upper inner cylindricalhousing wall 30, the lower end 31 of which constitutes an upper housingflow control corner at the upper end of an elongate internalcircumferential exhaust groove 32 of a substantially larger internaldiameter than the diameter of the inner cylindrical housing wall 34,which may be of the same internal diameter as the upper housing wall 30,the upper end of the lower wall being the housing lower flow controlcorner 33. The lower end 35 of the lower inner cylindrical housing wall34 provides a by-pass corner at the upper end of an enlarged internaldiameter circumferential by-pass groove 36.

The elongate hammer piston 20 includes an upper piston portion 37 havingan external diameter 37a conforming to the diameter of the upper innercylindrical housing wall 30, this upper piston portion terminating atthe upper end 38 of an external circumferential exhaust groove 39 of alesser external diameter than the upper piston portion 37. This externalexhaust groove terminates at a lower piston portion 40 having anexternal diameter conforming to the internal diameter of the lower innercylindrical housing wall 34. Below its lower piston portion 40, thehammer is of a reduced external diameter 41, providing a downwardlyfacing shoulder 42 which may, upon removal of the anvil bit C from thehousing 10, engage a limit ring 43 mounted in the housing section 14, toprevent the piston 20 from inadvertently dropping out of the housingstructure. The hammer piston extends upwardly to a substantial distanceabove its upper piston portion 37, having a plurality ofcircumferentially spaced relief spaces 44 which may be formed byelongate chords 45 in the hammer portion extending from the upper pistonportion 37 to the upper end 46 of the latter, there beingcircumferentially spaced elongate arcuate sections 47 between the chords45 having the same external diameter as the upper piston portion 37 andassisting in guiding the hammer piston 20 in its reciprocation withinthe housing section 14.

When the hammer piston 20 is at the lower end of its stroke, as shown inFIGS. 1a, 1b, a flow control piston corner 50 at the upper end of thepiston portion 37 is spaced below the upper housing flow control corner31, allowing air in the housing above the piston 20 to flow down throughthe passage 44 and into the internal circumferential exhaust groove 32,around the upper piston portion 37, then into radial exhaust ports 51,formed through the hammer piston below its intermediate piston wall 52,that communicate with an elongate central piston cavity 53 into which anexhaust tube 54 extends upwardly from the anvil 18, the tube forming acontinuation of the exhaust passage 53 and communicating with an exhaustpassage 55 through the anvil and through one or a plurality of exhaustpassages 56 extending downwardly through the bit 21 and openingoutwardly thereof for the purpose of enabling the drilling fluid to flowinto the bore hole D for removing the cuttings from the bottom E of thehole. The tube 54 makes a slidable seal with the wall 53a of the pistoncavity 53, being secured to the anvil 18 by a lower outwardly extendingtube flange 57 being received within an inner circumferential groove 58in the anvil. The tube may be made of an elastic material, such asDelrin, which permits it to be inserted within the anvil passage, theflange 57 contracting sufficientlyuntil it is opposite thecircumferential groove 58, whereupon the tube flange can snap outwardlyinto the groove 58 and thereby lock the tube 54 to the anvil 18.

When the piston 20 is shifted upwardly within the housing on its returnstroke, the return air corner 60 at the lower end of the lower pistonportion 40 will be disposed above the housing lower flow control corner33, whereupon the compressed air below the piston can exhaust into theinternal circumferential housing groove 32 and flow through the exhaustports 51 and exhaust passages 53, 55, 56 to the bottom E of the borehole. At this time, the upper flow control piston corner 50 will bedisposed above the upper housing flow control corner 31, which will sealthe upper piston portion 37 against the upper inner cylindrical housingwall 30, whereupon compressed air can drive the piston 20 downwardly onits hammer or power stroke. When the return air corner 60 moves belowthe housing lower flow control corner 33, the air below the piston andwithin the housing, which remains after the lower piston portion 40 isclosed within the lower end of the cylindrical housing wall 34, issubject to compression, but such air will be at a relatively lowpressure.

In the event the apparatus is elevated to raise the bit 21 from thebottom E of the hole, as shown in the aforementioned apparatus, the bitwill drop downwardly until its upper anvil head flange 110 engages theupper ends of the segments or keys 28; This will allow the upper pistonby-pass corner 62 to shift below the housing by-pass corner 35 at thelower end of the lower inner cylindrical housing wall 34, the upper flowcontrol piston corner being well below the upper housing flow controlcorner. Accordingly, compressed air above the piston can flow throughthe passages 44 and the internal circumferential exhaust groove 32 intothe air by-pass groove 36 below the lower housing wall 34, the airpassing downwardly through the passages 63 in the upper portion of theanvil rotary drive member and into the by-pass passages 64 past a headsealing portion 66 within the drivemember 15 and into elongate reliefgrooves 67 extending downwardly through the lower end of the drivemember 15. When the anvil 18 is in its upper position within the housingand with the bit shoulder 25 engaging the lower end 24 of the drivemember 15, the head sealing portion 66 seals against the periphery 68 ofthe anvil below its elongate grooves 27 in which the segments or keys 28are positioned. To facilitate such sealing, the head portion 66 may havea plurality of longitudinally spaced internal labyrinth seal grooves 69formed therein.

Compressed air for reciprocating the hammer piston passes downwardlythrough the string of drill pipe B and into the upper housing sub 11,flowing past a downwardly opening check valve 70 which may be in theform of a ball 71 received within a valve body 72 mounted in acounterbore 73 in the sub, the ball being movable upwardly to engage acompanion seat 74 surrounding a central passage 75 through the body, thedownward movement of the ball being limited by its engagement withcircumferentially spaced feet 76 extending inwardly fron the body. Withair being pumped downwardly through the apparatus, the ball7l engagesthe feet 76 and the air can flow around the ball and between the feetand into a central passage 77 in the housing sub.

The inlet air under pressure is caused to flow alternately into thehousing below the piston 20 and the housing above the piston, to effectreciprocation of the hammer piston. A housing inlet and valve tube 78are mounted in the sub passage 77, projecting downwardly from the sub orhead 11 and into an upper elongate central piston cavity or chamber 79above the intermediate piston wall 52, which separates the upper chamber79 from the lower chamber 53. The tube 78 is secured in the sub by anupper external flange 80 on the tube fitting within a companion internalcircumferential groove 81 in the sub. The inlet tube is made of aflexible material, such as. Delrin, which permits the upper portion ofthe tube to be deflected inwardly of the sub passage 77 below thecircumferential groove 81, and when the flange becomes aligned with thegroove, the latter inherently expands outwardly into the groove tosecure the tube to the sub 11. The elastic nature of the tube is suchthat it also provides a slidable seal with the inner walls of the piston20, as explained hereinbelow.

The piston has an elongate upper cylindrical surface 82 opening throughits upper end 46 and terminating at an inner, upper flow control pistoncorner 83, which is the upper end portion of an elongate internalcircumferential impact passage groove 84 having a substantially largerinternal diameter than the inside diameter of the upper piston portion82. The circumferential impact passage groove 84 terminates at anintermediate inner cylindrical piston wall 85, which may have the sameinternal diameter as the upper cylindrical piston wall 82, theintermediate wall terminating at an internal circumferential returnpassage groove 86 formed in the piston and terminating at a lower flowcontrol piston corner 87, which is the upper end of a lower internalpiston seal wall portion 88 that forms a bore extending between theintermediate pistion wall 52 and the corner 87. The inlet tube 78 has anupper external cylindrical sealing surface 89 relatively slidablysealable with the upper piston wall 82 and terminating in an externalcircumferential inlet groove 90 communicating with radial inlet ports 91that open to the central inlet passage 92 through the tube. Below thiscircumferential inlet groove 90, the tube is formed with an intermediatecylindrical sealing surface section 93 slidably and sealingly engageablewith the intermediate inner cylindrical piston wall and also with thelower piston wall 88.

When the piston 20 is in its lowermost operative position, with thedrill bit 21 pressed against the bottom E of the bore hole D, compressedair can flow downwardly through the inlet passage 92, discharging intothe circumferential return passage 86 that communicates with the upperportion of one or more longitudinal return passages 95 extendingdownwardly through the hammer piston and opening outwardly through itslower end 96. When the hammer piston 20 moves upwardly within thehousing 10 and along the inlet tube 78, the lower flow control pistoncorner 87 shifts upwardly over the lower flow control housing tubecorner 93a to interrupt communication between the inlet passage 92 andthe return passages 95, continued upward movement of the piston thenplacing the inner upper flow control piston corner 83 above the upperflow control housing tube corner 98, which then allows compressed air toflow from the inlet passage 92 through the ports 91 into thecircumferential inlet groove into the internal circumferential impactpassage groove 84 and thence in the housing above the upper end 46 ofthe piston. At this time, the upper piston portion 50 will have movedpartially above the upper housing flow control corner 31, so that theair under pressure between the upper end 46 of the piston and thehousing sub or head 11 can act downwardly on the piston, urging it in adownward direction.

The piston 20 will be shifted downwardly until the upper flow controlpiston corner 83 moves below the flow control housing tube corner 98,which shuts off air driven against the upper face 100 of the anvil todeliver an impact blow to the impact bit C. As the piston nears the endof its downward stroke, the lower flow control piston corner 87 willmove below the lower flow control housing tube corner 93a, therebyallowing the compressed air to flow from the inlet passage 92 into theupper piston cavity 79 and internal circumferential return passagegroove 86, passing downwardly through the longitudinal return passages95 to the lower end of the piston, such air then moving the piston in anupward direction, until the lower flow control piston corner 87 passesupwardly beyond the lower flow control housing tube corner 93a, onceagain, to shut off the flow of air into the return passages 95. Whenthis occurs, the outer upper flow control piston corner 50 moves abovethe upper housing flow control corner 31 to shut off the exhaust of airfrom the housing region above the piston 20, the compressed air belowthe piston expanding and driving the hammer piston upwardly toward thehead 11 of the housing. Before reaching the head 11, the inner upperflow control piston corner 83 will have shifted upwardly along the tube78 to a position above the upper flow control housing tube corner 98,allowing air under pressure to pass from the inlet passage 92 throughthe impact passage grooves 90, 84 to a position in the housing above thepiston 20.

The upward travel of the piston is cushioned by the compression of theair remaining in the housing above the piston. However, the pistion willstill move upwardly sufficiently to place the lower corner 60 of thelower piston portion 40 above the housing lower flow control corner 33,which then permits the compressed air below the piston to travel intothe internal circumferential exhaust groove 32 and through the exhaustports 51 into the exhaust passages 53, 55, 56 for discharge from thedrill bit. The compressed air in the housing structure above the pistonthen expands to drive the piston downwardly, and the foregoing cycle ofoperating is repeated, the piston reciprocating to deliver repeatedimpact blows against the anvil portion 18 of the anvil bit C, while thedrill string B and the entire apparatus A is being rotated, to insurethat the drilling or cutting elements 22 will cover substantially theentire cross-sectional area of the bore hole bottom E.

When it is desired to pump compressed air through the apparatus whilethe drill bit 21 is off bottom, elevation of the apparatus A will causethe impact bit C to drop downwardly along the housing until the upperanvil head 110 engages the upper ends of the keys 28. The piston 20 willalso drop downwardly until its bypass corner 62 is below the by-passcorner 35 of the housing 10, the upper corner 62 of the piston beingdisposed below the upper end of the internal circumferential groove 36.Accordingly, compressed air flowing downwardly through the drill stringB and into the inlet passage 92 can pass through the inlet ports 91 andupwardly between the tubing and the upper seal portion 82 to a positionabove the piston, then flowing downwardly through the passages 44 andinto the internal circumferential exhaust groove 32, flowing between theexternal circumferential exhaust groove 39 in the piston and the opposedlower inner cylindrical housing wall 34 into the enlarged diametergroove 36 below the inner cylindrical housing wall, then passing throughthe passages 63, 64, 67 to the exterior of the bit 21. Since the pathjust described is open, compressed air cannot remain below the piston20, which might otherwise tend to cause the piston to continuereciprocating andcyling in the housing 10. It is also evident that thecompressed air being pumped through the apparatus will also flow throughthe exhaust ports 51 and the exhaust 53, 55, 56 and downwardly throughthe anvil bit C.

When the piston 20 is on its power stroke. air will be compressed belowthe piston, as pointed out above, because of the sealing of the lowerpiston portion 40 against the lower inner cylindrical housing wall 34and the sealing of the head portion 66 against the periphery of theanvil 18. However, air under pressure is always present within the uppercentral piston cavity or chamber 79, acting over the cross-sectionalarea W of such chamber, and continuing to exert its force to overcomethe pressure acting upwardly over the piston and tending to elevate it.Thus, the hammer piston 20 will strike its impact blow upon the upperend of the anvil with a greater force, in view of the overcoming ofaportion of the resisting force offered by the compressed air actingupwardly over the cross-sectional area R across the lower portion of thepiston, such area existing between the periphery of the exhaust tube 54and the lower inner cylindrical housing wall 34.

On its power stroke, the compressed air acts over the fullcross-sectional area S of the upper piston portion, which is the samearea as the area across the inner cylindrical housing wall 30. It isacting downwardly over the cross-sectional area of the piston betweenthe pe riphery of the upper flow control tubeand the upper innercylindrical housing wall 30, and also over the area W across the centralpiston cavity or chamber 79 During the return stroke, the compressed airis acting upwardly over the piston over the area R, which is less thanthe full cross-sectional area S, but such full area is not needed forthe purpose of returning the piston under comparatively little loadtoward the upper end of its stroke.

As described above, the exhaust tube or sleeve 54 is made of an elasticmaterial, which is a suitable synthetic resin such as Delrin. Thissleeve must make a slidable seal with the wall 53a .of the piston cavity53 to prevent or minimize leakage of air between the tube and the wall53a. Because of manufacturing tolerances, a perfect alignment betweenthe hammer piston 20 and the anvil 18 may not exist. Accordingly, as thepiston approaches the anvil and impacts thereagainst, it imposes alateral force on the exhaust sleeve 54. If the exhaust tube made a closefit with the wall 580 of the anvil downwardly from its upper face 100,even a small amount of misalignment between the piston 20 and the anvilwould cause a high shearing stress to be imposed on the exhaust tube 54,resulting in fatigue failure of the exhaust tube after a relativelyshort period of use of the apparatus.

The above difficulty is overcome in the apparatus illustrated byproviding relief between the exterior of the exhaust tube or sleeve 54and the wall 580 of the anvil 18, such relief extending downwardly fromthe upper anvil face 100. As shown, a counterbore 58a is provided in theanvil that extends downwardly from its upper face 100 to a substantialextent, which, by way of example, is of the order of about l inch. Inview of the counterbore, any misalignments between the piston and theanvil 18 will prevent the high stresses from occurring on the tubesubstantially in the plane of the upper face 100 of the anvil. Instead,the exhaust sleeve 54 can readily flex or bend about the base 58b of thecounterbore, which acts as a fulcrum point, particularly in view of theelastic material from which the exhaust sleeve 54 is made. The bendingstresses to which the tube 54 is subjected as a result of misalignmentbetween the piston 20 and the anvil 18 are maintained at a comparativelylow value, which prevents the exhaust sleeve 54 from fatigue failure.

As previously indicated, during drilling the drill pipe is rotated in aright hand direction, and such rotation is transmitted to the anvil bit18 through the spline-like connection 26 between the drive member 15 andthe anvil 18, through the drive segments 28 which are disposed in theanvil slots 27 .and the windows 29 in the drive member 15. Thestructural arrangement of the present drive connection is such that therotary forces transmitted through the connection do not impose anyoutward camming action on the segments, in either direction of rotation,thereby minimizing wear and preventing galling of the segments or thehousing. In addition, the structural arrangement of the drive connectionis such that the contact area betweenthe segments and the anvil ismaximized for strength in the direction of rotation during drilling. Thesegments also cooperate with the anvil to provide an air flow passageduring circulation, as described above.

Referring to FIG. 2 it will be seen that in order to accomplish theabove-noted advantages, in this illustrative form, the side walls 27a ofthe segments 28 and the opposed walls 27b of the groove 27 are disposedon planes which are substantially radial, though actually off radial,being parallel, and perpendicular to the tangent 18 of the anvil l8, andthe walls 290 of the window 29 of the driver portion 15 of the housingare also parallel and coplanar with the slot walls 2712. Thus, no radialforce component is applied to the segments 28 forcing them outwardlyinto binding engagement with the cylindrical inner wall of the housing16. Indeed, the angle L between the confronting walls 27b, 29a and 27aand a true radial plane R1 is such that the segments are inherentlyforced inwardly by the torque transmitted therethrough.

In addition, in order to provide an increased section of the anvil 18for transmitting torque while drilling, the center line of the segments28 and the slot 27 are parallel to the radius R2 but offset in adirection opposite to the direction of drilling rotation, as indicatedby the arrow D, so that the wall 27b opposing the direction of drillingrotation is wider than the other wall 27b. This latter wall 27b needonly take the force transmitted in the direction of the arrow BO whenthe bit anvil 18 is held stationary and the housing 10 rotated to theleft to break out the thread 30d which connects the housing 16 and thedriver 15.

I claim:

1. ln hammer drilling apparatus comprising: a housing structureconnectible to a drill string and including a housing section and adrive member detachably secured to and surrounded by said housingsection; an

anvil in the housing structure; a' piston reciprocable in said housingstructure for intermittently impacting against said anvil; said anvilhaving a plurality of circumferentially spaced, longitudinal recessesformed by side walls disposed on generally radial opposed planes; saiddrive member having circumferentially spaced openings therein extendingcompletely through said drive member, said openings also being formed byside walls disposed on generally radially opposed planes; drive segmentsin said recesses and openings and having side walls engaged by saidwalls of said anvil and said drive member; said housing sectionsurrounding said drive member, openings and segments to close saidopenings, said housing section engaging said segments to retain saidsegments in said recesses and openings.

2. In apparatusas defined in claim I; said anvil recesses being longerthan said segments to enable said anvil to shift longitudinally in saidhousing structure and along said segments.

3. In apparatus as defined in claim 1; said segments being uniformlyspaced from each other circumferentially of said housing structure.

4. In hammer drilling apparatus comprising: a housing structureconnectible to a drill string; an anvil in the housing structure; apiston reciprocable in said housing structure for intermittentlyimpacting against said anvil; drive means for transmitting rotary motionfrom said housing structure to said anvil including a drive segmentinterposed between said anvil and said hous ing, and generally radiallyprojecting walls on said segment, on said anvil and on said housing fortransmitting torque between said anvil and said housing withoutv forcingsaid segment outwardly into engagement with said housing; a plurality ofsaid drive means uniformly spaced from each other circumferentially ofsaid housing structure, each of said segments being on a center linespaced from and parallel to a radial plane of said anvil.

5. In hammer drilling apparatus comprising: a housing structureconnectible to a drill string; an anvil in the housing structure; apiston reciprocable in said housing structure for intermittentlyimpacting against said anvil; drive means for transmitting rotary motionfrom said housing structure to said anvil including a drive segmentinterposed between said anvil and said housing, and generally radiallyprojecting walls on said segment, on said anvil and on said housing fortransmitting torque between said anvil and said housing without forcingsaid segment outwardly into engagement with said housing; said segmenthaving an air passage extending longitudinally therethrough.

6. In apparatus as defined in claim 1; said walls being disposed onparallel planes perpendicular to a tangent of said anvil.

' 7. In apparatus as defined in claim 4; said walls being disposed onparallel planes perpendicular to a tangent of said anvil.

8. In rotary hammer drilling apparatus: a housing structure connectibleto a drill string and including a housing section and a drive memberdetachably secured to and surrounded by said housing section; an anvilbit shiftable axially in said housing structure; a hammer pistonreciprocable in said housing structure for intermittently impacting uponthe upper portion of said anvil bit; said anvil bit having a pluralityof circumferentially spaced longitudinally extended recesses formed byside walls disposed on generally radial opposed planes; said drivemember having circumferentially spaced openings therein extendingcompletely through said drive member, said openings also being formed byside walls disposed on said generally radial opposed planes; drivesegments in said recess and openings and having side walls engaged bysaid walls of said anvil bit and said drive member; said housing sectionsurrounding said drive member, openings and segments to close saidopenings, said housing section engageing said segments to retain saidsegments in said recesses and openings.

9. In apparatus as defined in claim 8; the lower end of said drivemember engaging said anvil bit to transmit drilling weight thereto; sealmeans between said anvil bit and drive member to prevent fluid leakagetherebetween when the lower end of said drive member engages said anvilbit; means providing a fluid by-pass between said anvil bit and drivemember upon elevation of said drive member with respectto said anvilbit; said by pass including said recesses in said anvil bit; and saidsegments having a longitudinal passage therethrough.

10. In apparatus as defined in claim 8; said side walls of said recessesand said openings being on parallel planes perpendicular to the tangentof said anvil bit.

11. In rotary hammer drilling apparatus: a housing structure connectibleto a drill string and including a drive member detachably secured to ahousing section; an anvil bit shiftable axially in said housingstructure; a hammer piston reciprocable in said housing structure forintermittently impacting upon the upper portion of said anvil bit; saidanvil bit having a plurality of circumferentially spaced longitudinallyextended recesses formed by side walls disposed on generally radialopposed planes; said drive member having circumferentially spacedopenings therein also formed by side walls disposed on said generallyradial opposed planes; and drive segments in said recesses and openingsand having side walls engaged by said walls of said anvil bit and saiddrive member; said recesses and said openings having centers located inplanes parallel to and offset from a radial plane of said anvil bit in adirection opposite to the direction of drilling rotation of theapparatus 12. In apparatus as defined in claim 11; said housing and saiddrive member having a threaded connection made up in the direction ofdrilling rotation of the apparatus.

13. In apparatus as defined in claim 11; said side walls of saidrecesses and said openings being on parallel planes perpendicular to thetangent of said anvil bit, said housing and said drive member having athreaded connection made up in the direction of drilling rotation of theapparatus.

14. In apparatus as defined in claim 11; said side walls of saidrecesses and said openings being on parallel planes perpendicular to thetangent of said anvil bit; said housing and said drive member having athreaded connection made up in the direction of drilling rotation of theapparatus; the lower end of said drive member engaging said anvil bit totransmit drilling weight thereto; seal means between said anvil bit anddrive member to prevent fluid leakage therebetween when the lower end ofsaid drive member engages said anvil bit; means providing a fluidby-pass between said anvil bit and drive member upon elevation of saiddrive member with respect to said anvil bit; said by-pass including saidrecesses in said anvil bit;'and said segments having a longitudinalpassage therethrough.

15. In rotary hammer drilling apparatus: a housing structure connectibleto a drill string and including a housing section and a drive memberdetachably secured to and surrounded by said housing section; an anvilbit shiftable axially in said housing structure; said anvil bit having aplurality of circumferentially spaced longitudinally extended recessesformed by side walls disposed on generally radial opposed planes; saiddrive member having circumferentially spaced openings therein extendingcompletely through said drive member, said openings also being formed byside walls disposed on said generally radial opposed planes; drivesegments in said recesses and openings and having side walls engaged bysaid walls of said anvil bit and said drive member; said housing sectionsurrounding said drive member, openings and segments to close saidopenings, said housing action engaging said segments to retain saidsegments in said recesses and openings.

16. In rotary hammer drilling apparatus: a housing structure connectibleto a drill string and including a drive member detachably secured to ahousing section; an anvil bit shiftable axially in said housingstructure; said anvil bit having a plurality of circumferentially spacedlongitudinally extended recesses formed by side walls disposed ongenerally radial opposed planes; said drive member havingcircumferentially spaced openings therein also formed by side wallsdisposed on said generally radial opposed planes; and drive segments insaid recesses and openings and having side walls engaged by said wallsof said anvil bit and said drive member; the lower end of said drivemember engaging said anvil bit to transmit drilling weight thereto; sealmeans between said anvil bit and drive member to prevent fluid leakagetherebetween when the lower end of said drive member engages said anvilbit; means providing a fluid by-pass between said anvil bit and drivemember upon elevation of said drive member with respect to said anvilbit; said by-pass including said recesses in said anvil bit; and saidsegments having a longitudinal passage therethrough.

17. In apparatus as defined in claim 15; said side walls of saidrecesses and said openings being on parallel planes perpendicular to thetangent of said anvil bit.

18. In rotary hammer drilling apparatus: a housing structure connectibleto a drill string and including a drive member detachably secured to ahousing section; an anvil bit shiftable axially in said housingstructure; said anvil bit having a plurality of circumferentially spacedlongitudinally extended recesses formed by side walls disposed ongenerally radial opposed planes; said drive' member havingcircumferentially spaced openings therein also formed by side wallsdisposed on said generally radial opposed planes; and drive segments insaid recesses and openings and having side walls engaged by said wallsof said anvil bit and said drive member; said recesses and said openingshaving centers located in planes parallel to and offset from a radialplane of said anvil bit in a direction opposite to the direction ofdrilling rotation of the apparatus.

19. In apparatus as defined in claim 18; said side walls of saidrecesses and said openings being on parallel planes perpendicular to thetangent of said anvil bit, said housing and said drive member having athreaded connection made up in the direction of drilling rotation of theapparatus.

1. In hammer drilling apparatus comprising: a housing structureconnectible to a drill string and including a housing section and adrive member detachably secured to and surrounded by said housingsection; an anvil in the housing structure; a piston reciprocable insaid housing structure for intermittently impacting against said anvil;said anvil having a plurality of circumferentially spaced, longitudinalrecesses formed by side walls disposed on generally radial opposedplanes; said drive member having circumferentially spaced openingstherein extending completely through said drive member, said openingsalso being formed by side walls disposed on generally radially opposedplanes; drive segments in said recesses and openings and having sidewalls engaged by said walls of said anvil and said drive member; saidhousing section surrounding said drive member, openings and segments toclose said openings, said housing section engaging said segments toretain said segments in said recesses and openings.
 2. In apparatus asdefined in claim 1; said anvil recesses being longer than said segmentsto enable said anvil to shift longitudinally in said housing structureand along said segments.
 3. In apparatus as defined in claim 1; saidsegments being uniformly spaced from each other circumferentially ofsaid housing structure.
 4. In hammer drilling apparatus comprising: ahousing structure connectible to a drill string; an anvil in the housingstructure; a piston reciprocable in said housing structure forintermittently impacting against said anvil; drive means fortransmitting rotary motion from said housing structure to said anvilincluding a drive segment interposed between said anvil and saidhousing, and generally radially projecting walls on said segment, onsaid anvil and on said housing for transmitting torque between saidanvil and said housing without forcing said segment outwardly intoengagement with said housing; a plurality of said drive means uniformlyspaced from each other circumferentially of said housing structure, eachof said segments being on a center line spaced from and parallel to aradial plane of said anvil.
 5. In hammer drilling apparatus comprising:a housing structure connectible to a drill string; an anvil in thehousing structure; a piston reciprocable in said housing structure forintermittently impacting against said anvil; drive means fortransmitting rotary motion from said housing structure to said anvilincluding a drive segment interposed between said anvil and saidhousing, and generally radially projecting walls on said segment, onsaid anvil and on said housing for transmitting torque between saidanvil and said housing without forcing said segment outwardly intoengagement with said housing; said segment having an air passageextending longitudinally therethrough.
 6. In apparatus as defined inclaim 1; said walls being disposed on parallel planes perpendicular to atangent of said anvil.
 7. In apparatus as defined in claim 4; said wallsbeing disposed on parallel planes perpendicular to a tangent of saidanvil.
 8. In rotary hammer drilling apparatus: a housing structureconnectible to a drill string and including a housing section and adrive member detachably secured to and surrounded by said housingsection; an anvil bit shiftable axially in said housing structure; ahammer piston reciprocable in said housing structure for intermittentlyimpacting upon the upper portion of said anvil bit; said anvil bithaving a plurality of circumferentially spaced longitudinally extendedrecesses formed by side walls disposed on generally radial opPosedplanes; said drive member having circumferentially spaced openingstherein extending completely through said drive member, said openingsalso being formed by side walls disposed on said generally radialopposed planes; drive segments in said recess and openings and havingside walls engaged by said walls of said anvil bit and said drivemember; said housing section surrounding said drive member, openings andsegments to close said openings, said housing section engageing saidsegments to retain said segments in said recesses and openings.
 9. Inapparatus as defined in claim 8; the lower end of said drive memberengaging said anvil bit to transmit drilling weight thereto; seal meansbetween said anvil bit and drive member to prevent fluid leakagetherebetween when the lower end of said drive member engages said anvilbit; means providing a fluid by-pass between said anvil bit and drivemember upon elevation of said drive member with respect to said anvilbit; said by-pass including said recesses in said anvil bit; and saidsegments having a longitudinal passage therethrough.
 10. In apparatus asdefined in claim 8; said side walls of said recesses and said openingsbeing on parallel planes perpendicular to the tangent of said anvil bit.11. In rotary hammer drilling apparatus: a housing structure connectibleto a drill string and including a drive member detachably secured to ahousing section; an anvil bit shiftable axially in said housingstructure; a hammer piston reciprocable in said housing structure forintermittently impacting upon the upper portion of said anvil bit; saidanvil bit having a plurality of circumferentially spaced longitudinallyextended recesses formed by side walls disposed on generally radialopposed planes; said drive member having circumferentially spacedopenings therein also formed by side walls disposed on said generallyradial opposed planes; and drive segments in said recesses and openingsand having side walls engaged by said walls of said anvil bit and saiddrive member; said recesses and said openings having centers located inplanes parallel to and offset from a radial plane of said anvil bit in adirection opposite to the direction of drilling rotation of theapparatus.
 12. In apparatus as defined in claim 11; said housing andsaid drive member having a threaded connection made up in the directionof drilling rotation of the apparatus.
 13. In apparatus as defined inclaim 11; said side walls of said recesses and said openings being onparallel planes perpendicular to the tangent of said anvil bit, saidhousing and said drive member having a threaded connection made up inthe direction of drilling rotation of the apparatus.
 14. In apparatus asdefined in claim 11; said side walls of said recesses and said openingsbeing on parallel planes perpendicular to the tangent of said anvil bit;said housing and said drive member having a threaded connection made upin the direction of drilling rotation of the apparatus; the lower end ofsaid drive member engaging said anvil bit to transmit drilling weightthereto; seal means between said anvil bit and drive member to preventfluid leakage therebetween when the lower end of said drive memberengages said anvil bit; means providing a fluid by-pass between saidanvil bit and drive member upon elevation of said drive member withrespect to said anvil bit; said by-pass including said recesses in saidanvil bit; and said segments having a longitudinal passage therethrough.15. In rotary hammer drilling apparatus: a housing structure connectibleto a drill string and including a housing section and a drive memberdetachably secured to and surrounded by said housing section; an anvilbit shiftable axially in said housing structure; said anvil bit having aplurality of circumferentially spaced longitudinally extended recessesformed by side walls disposed on generally radial opposed planes; saiddrive member having circumferentially spaced openings therein extendingcompletelY through said drive member, said openings also being formed byside walls disposed on said generally radial opposed planes; drivesegments in said recesses and openings and having side walls engaged bysaid walls of said anvil bit and said drive member; said housing sectionsurrounding said drive member, openings and segments to close saidopenings, said housing action engaging said segments to retain saidsegments in said recesses and openings.
 16. In rotary hammer drillingapparatus: a housing structure connectible to a drill string andincluding a drive member detachably secured to a housing section; ananvil bit shiftable axially in said housing structure; said anvil bithaving a plurality of circumferentially spaced longitudinally extendedrecesses formed by side walls disposed on generally radial opposedplanes; said drive member having circumferentially spaced openingstherein also formed by side walls disposed on said generally radialopposed planes; and drive segments in said recesses and openings andhaving side walls engaged by said walls of said anvil bit and said drivemember; the lower end of said drive member engaging said anvil bit totransmit drilling weight thereto; seal means between said anvil bit anddrive member to prevent fluid leakage therebetween when the lower end ofsaid drive member engages said anvil bit; means providing a fluidby-pass between said anvil bit and drive member upon elevation of saiddrive member with respect to said anvil bit; said by-pass including saidrecesses in said anvil bit; and said segments having a longitudinalpassage therethrough.
 17. In apparatus as defined in claim 15; said sidewalls of said recesses and said openings being on parallel planesperpendicular to the tangent of said anvil bit.
 18. In rotary hammerdrilling apparatus: a housing structure connectible to a drill stringand including a drive member detachably secured to a housing section; ananvil bit shiftable axially in said housing structure; said anvil bithaving a plurality of circumferentially spaced longitudinally extendedrecesses formed by side walls disposed on generally radial opposedplanes; said drive member having circumferentially spaced openingstherein also formed by side walls disposed on said generally radialopposed planes; and drive segments in said recesses and openings andhaving side walls engaged by said walls of said anvil bit and said drivemember; said recesses and said openings having centers located in planesparallel to and offset from a radial plane of said anvil bit in adirection opposite to the direction of drilling rotation of theapparatus.
 19. In apparatus as defined in claim 18; said side walls ofsaid recesses and said openings being on parallel planes perpendicularto the tangent of said anvil bit, said housing and said drive memberhaving a threaded connection made up in the direction of drillingrotation of the apparatus.